The uniting of haploid chromosome sets from an egg and a sperm initiates the formation of a new diploid organism and triggers the onset of mitosis in embryos. I propose to analyze parentally-encoded gene products needed for these very early embryonic events in Drosophila. Specifically, we will continue our molecular genetic analysis of the fs(1)Ya gene, and extend our studies to gene products that interact with or control it. Function of the fs(1)Ya gene is required for the very first (gonomeric) division and possibly for subsequent mitotic divisions in early embryos. The fs(1)Ya gene encodes a maternally-specified nuclear envelope protein essential for the integrity for the nuclear lamina. The protein's association with the nuclear envelope is cell cycle stage dependent. Our studies will address the role and interactions of parental macromolecules, and of the nuclear envelope, in early embryonic mitosis. We will complete the characterization of embryos produced by fs(1)Ya mutant mothers by examining nuclear envelopes and mitotic components in these embryos. Then we will investigate biochemical characteristics suggested by the sequence of the fs(1)Ya protein and the phenotypes of fs(1)Ya null mutants. These include: whether the fs(1)Ya protein can be phosphorylated, whether it can bind to lamins and whether it can bind to DNA. The sequence alterations in fs(1)Ya mutations will be determined and correlated with the subcellular distribution of the mutant proteins and the mutant phenotypes to determine functional domains of the protein. In order to place fs(1)Ya action in a temporal order with the action of other parental gene products controlling mitosis, we will continue to examine the phenotypes of double mutants of fs(1)Ya2 and "early arrest" mutations. We will also examine the fs(1)Ya protein in embryos of mutants in genes that function in early mitoses. To identify genes whose products directly interact with fs(1)Ya protein, we will screen for dominant suppressors of fs(1)Ya mutations. In future years, the genes identified in the suppressor screens will be analyzed and the nature of the interactions between their products and fs(1)Ya protein determined. The proposed studies will allow a molecular genetic dissection of macromolecules needed for pronuclear fusion and initiation of mitosis in embryos. Simultaneously, they will permit the first genetic dissection of a non-lamin nuclear envelope component, and its developmental function, in an animal.